It is well known in the automotive arts to provide internal combustion engines with activation/deactivation mechanisms for varying the lift and timing of some of the engine combustion valves. For example, a V-6 engine may be modified such that one bank of three cylinders may be deactivated under conditions of low demand by keeping closed the intake and exhaust valves of the three cylinders via a switching mechanism, thus allowing a vehicle to operate on essentially a three-cylinder engine. The resulting fuel savings can be substantial. For another example, through a valve lift switching mechanism, the valves may be provided with a relatively low lift to conserve fuel under conditions of low demand and a higher lift when higher power is required.
The aforementioned switching mechanisms are commonly electrohydraulic. An oil control valve actuated by an electric solenoid feeds pressurized oil to, or withholds oil from, a plurality of spring-loaded hydraulically-actuated lock pin latching mechanisms disposed at some point in the valve train to control the resultant valve lift originated by the engine camshaft.
A known problem with hydraulic actuation of lock pins arises from an uncertainty of the lock pin position at the start of a valve lift event. For a variety of reasons, the pressure change dynamics in the switching gallery are not constant. The resulting variation can produce an undesirable behavior known in the art as “lock pin ejection”, which occurs occasionally because the motion of a lock pin cannot be controlled precisely with respect to the beginning of a lift event for a particular cylinder to assure full engagement/disengagement of the lock pin. This problem is aggravated by elevated engine speed, wherein a shorter time is available for lock pin engagement, and/or by a reduced number of independent control signals. A lock pin ejection occurs when there is insufficient lock pin engagement (“partial engagement”) with the receiver, at the time the cam initiates a lift event, to sustain the lift event. In such case, engagement is sufficient to only partially open the valve before the lock pin is ejected from engagement back to its unlocked position, resulting in an unplanned mode shift. Such ejections can lead to undesired durability issues for various components associated with the valve train mechanism.
Certain design variables can be optimized to minimize the percentage of switches in which an ejection takes place. However, it may not be possible to eliminate ejections totally. For example, it is advantageous to save on manufacturing cost by grouping a plurality of valve switching mechanisms, such as for three intake valves on one bank of a V-6 engine, under the control of a single oil control valve rather than providing a separate oil control valve and control mechanism for each valve train. Such valves might be numbered, for example, 1, 3, and 5. In the prior art, a switch command is always issued at a given point in an engine cycle (engine crank angle), for example, just before intake valve 1 is scheduled to begin a lift. Valve 1 is thus the initial valve to be switched. Intake valves 3 and 5 will be on other portions of their lift cycles, including being on a base circle portion of their individual cam lobes before another lift is required; hence, there is a high probability that the latching of the mechanisms for valves 3 and 5 will take place fully and without subsequent premature ejection. Thus, for the three valves, lock pin ejections will occur almost exclusively on the valve 1 valve train.
What is needed in the art is a means for distributing evenly the occurrences of lock pin ejection over all the valve trains controlled by a single oil control valve.
It is a principal object of the present invention to minimize durability issues arising from lock pin ejections on each switchable mechanism in a plurality of valve switchable mechanisms controlled by a single oil control valve by distributing lock pin ejections evenly over all the switchable mechanisms.